The invention relates to a device for detecting the presence of misting on a motor-vehicle window. A window of this type, such as the windscreen of the vehicle, is interposed between the outside and the passenger compartment of the vehicle.
A device for such detection generally comprises at least one input suitable for receiving information relating to a state of misting of the windscreen, as well as an output linked to a control module of an installation for heating, ventilating and/or air conditioning the passenger compartment of the vehicle. The control module issues a set-point value, as appropriate, for ventilating the windscreen, on the basis of the abovementioned information.
Known devices of this type usually include an optical measurement of the reflection of a beam on one face of the windscreen, on the passenger compartment side, in order to detect that it is misting up.
However, the beam illuminates only a localized region of the windscreen and it remains possible for a different region to be misted. Furthermore, it is often the case that stray light disturbs such optical measurements.
In the published European patent application EP 0718165, an interesting solution is proposed consisting in providing a device equipped with a dew-point sensor on the windscreen of the vehicle, or else a temperature probe accompanied by a humidity probe. However, such sensors are expensive and aggravate the cost of the detection.
The present invention aims to improve the situation.
According to one aspect of the invention there is provided a device for detecting a risk of misting being present on a motor-vehicle window, the said window being interposed between the outside and the passenger compartment of the vehicle, the device comprising:
at least a first and a second input for receiving at least first and second information, relating respectively to a temperature of the window and to a dew temperature in the passenger compartment of the vehicle,
a calculating module suitable for:
a) estimating a temperature of the window from at least the first information,
b) estimating a dew temperature in the passenger compartment of the vehicle from at least the second information, and
c) estimating a comparison between the temperature of the window and the dew temperature in order to deduce therefrom a risk of misting being present on the window,
as well as an output suitable for delivering a signal relating to a risk of misting being present.
The comparison between the temperature of the window and the dew temperature may be represented by a difference between these two temperatures, or else by a ratio between these temperatures.
According to one advantageous characteristic of the invention, the device further includes a memory configured to store dew-temperature values associated, according to a Mollier diagram, with predetermined humidity values. The calculating module is then configured to work with this memory with a view to estimating the dew temperature on the basis of a relative-humidity budget. This characteristic offers the advantage of dispensing with a dew-temperature sensor, which is particularly expensive and of relative reliability.
In one variant, the calculating module may be configured to estimate the dew temperature as a function of a humidity value, according to a predetermined equation. As in the preceding variant, this humidity value is preferably deduced from a relative-humidity budget.
In one preferred embodiment, the second input is suitable for being connected to a temperature sensor of a cold-air source of the installation. In practice, this cold-air source is formed by an evaporator of an air-conditioning loop which the installation includes. In the abovementioned relative-humidity budget, it is considered that the air leaving the evaporator is substantially saturated with humidity and can thus give access to the dew temperature. The calculating module is then configured to evaluate the dew temperature on the basis of information relating to this temperature of the cold-air source. Initially, the air of the passenger compartment is preferably considered to be saturated with humidity. Such an implementation advantageously makes it possible to reduce the risks of misting, at the cost of needlessly triggering ventilation of the windscreen (or of other windows of the vehicle).
In one developed embodiment, the relative-humidity budget takes account, moreover, of an initial temperature in the passenger compartment and a throughput of air blown into the passenger compartment. Advantageously, the device further includes inputs suitable for receiving information relating to a temperature in the passenger compartment and to a throughput of air blown into the passenger compartment.
In one further improved embodiment, the device further includes an input suitable for receiving information relating to humidity given off by the passengers of the passenger compartment, while the relative-humidity budget moreover takes account of average humidity, given off by the passengers. In practice, indicators of the presence of passengers could be provided, such as sensors in the seats of the passenger compartment or infrared sensors.
Advantageously, the abovementioned memory includes data relating to a predetermined value of a total volume of air in the passenger compartment, appearing in the abovementioned relative-humidity budget.
In one embodiment according to which the installation includes a device for recirculating air in the passenger compartment, the device according to the invention advantageously includes an input suitable for being connected to an actuator for adjusting the position of a recirculation flap, while the calculating module is configured to distinguish, in the relative-humidity budget, humidity of outside air blown into the passenger compartment and humidity of air recirculated in the passenger compartment, depending on the position of the recirculation flap.
As far as the estimating of the temperature of the window is concerned, the device according to the invention advantageously includes a plurality of inputs suitable for receiving information relating to a temperature and a speed of blown air, to an average temperature in the passenger compartment, to the speed of the vehicle and to an outside-air temperature.
In the French patent application FR-9806831 by the Applicant, a device is described which is capable of estimating a temperature of air blown into any region of the passenger compartment of a motor vehicle, solely on the basis of information relating to a temperature and a speed of air blown by the aeration vents of the passenger compartment, to an average temperature in the passenger compartment, to the speed of the vehicle and to an outside-air temperature. More particularly, the temperatures and speed of blown air can be deduced from a control of the actuators for setting a hot-air source and/or a cold-air source (for the temperature) and from a blower (for the speed) which the installation for heating, ventilating and/or air-conditioning the passenger compartment of the vehicle comprises. Such a control offers a saving on temperature and airspeed sensors.
As to the information relating to an average temperature in the passenger compartment, to the speed of the vehicle and to an outside-air temperature, these can be deduced from measurements by sensors currently used in the motor-vehicle field, and already serve, at least partly, to establish the abovementioned relative-humidity budget.
Thus, the use by the device according to the invention of the technique described in the application FR-9806831 advantageously makes it possible to estimate a (spatially) average temperature of the window, while saving on a plurality of temperature sensors, arranged at respective regions of the window and necessary for determining this average temperature.
The calculating module is then configured to estimate the temperature of the window on the basis of the temperature and of the speed of air blown onto the window, of the average temperature in the passenger compartment, of the speed of the vehicle and of the outside-air temperature.
In one developed embodiment, the device further includes an input suitable for being connected to a solar-flux sensor, and the calculating module is configured to estimate the temperature of the window by taking account of insolation of the window.
According to an advantageous characteristic of the invention, the output of the detection device is suitable for being connected to a module for control of an installation for heating, ventilating and/or air-conditioning the passenger compartment of the vehicle, in order to deliver a set-point value relating to a risk of misting being present.
In this respect in a second aspect, the invention provides installation for heating, ventilating and/or air conditioning the passenger compartment of a motor vehicle, the installation comprising a module for control of at least one item of equipment of the installation, configured to work with a device for detecting a risk of misting being present on a motor-vehicle window, the said window being interposed between the outside and the passenger compartment of the vehicle, the device comprising:
at least a first and a second input for receiving at least first and second information, relating respectively to a temperature of the window and to a dew temperature in the passenger compartment of the vehicle,
a calculating module suitable for:
a) estimating a temperature of the window from at least the first information,
b) estimating a dew temperature in the passenger compartment of the vehicle from at least the second information, and
c) estimating a comparison between the temperature of the window and the dew temperature in order to deduce therefrom a risk of misting being present on the window,
as well as an output suitable for delivering a signal relating to a risk of misting being present.
Such an installation advantageously includes a device for ventilating the window. The control module is then configured to work with the detection device, with a view to delivering a set-point value for ventilation of the window when the estimated difference between the temperature of the window and the dew temperature (which are associated with humidity values) is below a first threshold value.
In one more advanced variant, the installation includes a device for air conditioning the passenger compartment. The control module is then configured to work with the detection device, with a view to delivering a set-point value for air conditioning the passenger compartment when the estimated difference between the temperature of the window and the dew temperature is below a second threshold value.
Advantageously, the installation includes a device for heating the air blown onto the window. The control module is then configured to work with the detection device, with a view to delivering a set-point value for heating the air blown onto the window when the estimated difference between the temperature of the window and the dew temperature is below a third threshold value.
Advantageously, the installation further includes a device for recirculating air in the passenger compartment. The control module is then configured to work with the detection device, with a view to delivering a set-point value for letting outside air into the passenger compartment when the estimated difference between the temperature of the window and the dew temperature is below a fourth threshold value.
In a preferred embodiment, the installation includes an air-conditioning loop comprising an evaporator, as well as a temperature sensor, arranged in proximity to the evaporator and downstream of it in the direction of travel of an air flow intended to be blown into the passenger compartment. This sensor is suitable for being connected to the abovementioned second input of the detection device.
Thus, the detection device according to the invention advantageously needs no supplementary sensors by comparison with a conventional heating, ventilation and/or air-conditioning installation.